This invention relates generally to vent tools used in subterranean well bores and more particularly, but not by way of limitation, to a vent tool having a vent subassembly connectible below a packer and an actuator subassembly connectible above the packer but in association with the vent subassembly to communicate an operating action to the vent subassembly in response to an actuating differential pressure force existing between the annulus and the inner diameter of a tubing string to which the actuator subassembly is connected, which operating action is, even more particularly, communicated to a perforator to concurrently initiate firing of explosive charges within the perforator.
In perforating a subterranean formation intersected by a well bore, vent tools are sometimes used to surge the perforations which have been created in the formation by explosive charges in a perforating gun of a perforator. For example, a vent can be used with a tubing conveyed perforator which will be followed by a gravel pack. The formation will first be fabricated under a balanced condition with the vent closed. Thereafter, the vent will be opened to surge the perforation, after which fluid will be reversed out of the tubing and the assembly removed from the well bore. The well will then be gravel packed. Such a vent and perforator will be run into the well bore on a tubing string and generally used with a packer also connected as part of the tubing string. In this instance, the vent and the perforator are located below the packer in the tubing string.
The need for such type of vent tool is well known in the industry. Vents have been proposed or used which are pressure actuated. Some respond to a tubing pressure applied down through the tubing string to where the vent is located. Others respond to annular pressure in the "rathole" below the packer where the vent is located. Still others respond to a pressure differential created in the vent relative to a prepressurized chamber contained within the vent. All of these require use of a fluid pressure at the location where the vent is disposed, such as below a packer. This may require a relatively complex venting assembly or a relatively complex coupling for coupling to the packer. To obviate this complexity, there is the need for a vent tool which has a simplified construction easily connectible to a packer or into a tubing string and which can be actuated by a force existing or exerted from above the packer or, more broadly, at a location spaced from where the venting is to occur. This need calls for a unique coupling arrangement or operational relationship between the physically spaced venting structure and actuating structure. This uniqueness arises not only from the need to have the actuating structure respond to a force where it is located and then to communicate a resultant operation to the vent, but also to accommodate spacing differentials between the venting structure and the actuating structure. This coupling should be designed to facilitate relatively easy connecting and disconnecting between the venting and actuating structures.
Another desirable feature would be for the design to allow the venting structure to be interconnected or associated with the actuating structure after the packer (where used) and venting structure have been made into the tubing string and lowered through the mouth of the well bore. This would facilitate the making of the connections between the venting structure and the tubing string because the actuating structure would not at that time have to be also connected.
Another desirable feature would be to have some means for mechanically locking the vent structure open without requiring a sustained external force to be applied to the vent structure.
Still another desirable feature would be for the unique association between the venting and actuating structures to provide concurrent initiation of the firing of the perforator if one is connected into the tubing string.